Introduction Necrotizing autoimmune myositis (NAM) is an increasingly recognised myositis.¹ While diagnosis is primarily from muscle pathology, antibodies to signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl–coenzyme A reductase (HMGCR) are also associated.

Case A 67 year old woman presented with proximal weakness and elevated creatine kinase (CK) levels following a complicated AMI, CABG and commencement of atorvastatin. Muscle biopsy confirmed necrotizing myositis and SRP (not HMGCoAR) antibodies were positive. Recovery and rehabilitation was slow and her CK did not normalise for 12 months. She was treated with immunotherapy including intravenous immunoglobulin, oral and intravenous corticosteroids, azathioprine, and mycophenolate.

Residual hip, abdominal and truncal weakness remained, affecting her gait and posture. CK levels during this period remained normal. MRI demonstrated extensive paravertebral muscle loss with fatty replacement without oedema. Small myopathic units without active features were present on EMG.

Conclusion This case illustrates several important aspects of NAM, which remains a rare disorder. Recovery can be incomplete in up to 40%, especially if control is delayed.² In our opinion, normalisation of CK is an important target and may be necessary for full recovery, and rising CK may predict relapse.³ We suggest MRI and EMG of weak muscles may assist in distinguishing persisting myositis from ‘burnt-out’ disease, clarifying whether immunotherapy should be increased or not. However relapse on weaning immunosuppression remains frequent. While SRP antibodies in patients who had also taken statins has been previously reported, the quick sequential onset in this case suggests possible causality.

References

1. Mammen AL. Autoimmune Myopathies. Contin Lifelong Learn Neurol. 2016;22(6):1852–1870.

2. Watanabe Y, Uruha A, Suzuki S, et al. Clinical features and prognosis in anti-SRP and anti-HMGCR necrotising myopathy. J Neurol Neurosurg Psychiatry 2016;87(10):1038–1044.

3. Ramanathan S, Langguth D, Hardy TA, et al. Clinical course and treatment of anti-HMGCR antibody–associated necrotizing autoimmune myopathy. Neurol Neuroimmunol Neuroinflammation 2015;2:e96.